I think yes, but we never know it because their transaction is really secret. I think the illegal activites only for 1-5 transaction. it's make us hard to detect it.
As long as no one admits it that they are using bitcoin for their illegal activities, then we have no proof. Bitcoin transactions anonymity is the only thing we know that it could possibly be used in illegal activity.
Everything that has a value can be used in illegal activity and bitcoin is one of those.
Sure, But anonymity of bitcoin make have much problem for bitcoin, example: some countires,merchant,online store need to think againt to accept bitcoin become one of their legal payment. but it's for some time ago. I think for now, example: "for Europian Union,In October 2015, the European Court of Justice ruled that bitcoin transactions are exempt from consumption tax similarly as traditional cash.According to judges, the tax shouldn’t be charged because bitcoins should be treated as a means of payment."
Source:
https://en.wikipedia.org/wiki/Legality_of_bitcoin_by_countryWell, I think it's good progress for bitcoin. Yes you're right "Everything that has a value can be used in illegal activity and bitcoin is one of those", but.we must keep always positive thinking about it.